Electric-current transmission



Feb. 1,1927. 1,616,115?

W. J. ADAMS, JR

ELECTRIC CURRENT TRANSMISSION Filed Sept. l0. 1924 Cil potential for thethrough a resistance 10 which mav be of the Patented Feb. 1, 1927yUNITED STATES PATENT OFFICE.

WILLIAM J'. ADAMS, JR., OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRICCOM- PANY, INCORPORATED, 'OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

ELECTRIC-CURRENT TRANSMISSION.

.application led September 10, 1924. Serial No. 736,835.

This invention relates to transmission of etectricv currents and aims toprovide a ilexible line ot' propagation for them without unduly shuntingcurrent across the line of propagation and without permittingl undueinterference fromf extraneous electrical fields. An especial object isto lavoid such undue shunting effect and interference where the flexibleline of propagation comprises aV con ection between` impcdances whichare higi for alternating currents to be transmitted, as for instance aconnection between a condensertransmitter and an electron dischargea'mplier.`

In accordance with the invention. for connecting the impedances betweenwhich current is to be transmitted there is provided a. iexiible'electrical cord comprising tivo electrical conductors, one of which isarranged to shield the other from extraneous electrical fields, andinsulating means maintaining thecapacity and leakage resistance of thecord at such values as to substantially avoid deleteriously sbunting thecurrents to be transmitted.

'lhe single figure of the drawing shows one embodiment of the invention,with parts of the cord shown broken away to exhibit its internalstructure.

lu thc drawing the cord 2 is shown connecting a condenser transmitter '8to an electron tube amplifier 4. The space current battery 9 for thefirst stage of the amplifier is shown as supplying polarizing condensertransmitter order of 15 megohms. A resistance 1l, which may be of theorder of two megohms, and capacities'12 and 153, which may be of theorder of two microfarads form a filter to prevent fluctuations of thevoltage of battery 9 from affecting the transmitter 3.

The condenser transmitter 3 may be a telephone transmit-ter having acapacity, for example of the order of 400 micromicrofarads. Itsimpedance at speech frequencies will then he very high` and therefore itis shown connected directly to the grid of the input stage of theamplifier through a suitable blocking condenser l5 wit-hout tbeinterposition of a transformer. resistance 16 which may be of the orderot 15 megohms, isconnected across the grid and filament of the firststage of the amplifier. to maintain the grid at a constant negativeaverage potential.,

Any capacity between the conductors of the cord Connecting thetransmitter to the amplifier is in shunt with the transmitter, with`|respect to the amplifier, and therefore occasions transmission loss. Onaccount of the relatively low capacity of the transmitter itself, thisloss, when ordinary flexible cords of any considerable length are used,is quite large. The fiexible cord 2 is therefore constructed, asdescribed hereinafter, to have low capacity between its conductors'.Moreover. unless proper shielding` is employed, the deleterious effectof any inductive interference to which the conductors of the cordconnecting the Ytransmitter to the amplifier are subjected, due toextraneous electrical fields, may be pronounced because of the loWmagnitude of the voltages delivered to the input of the amplifier by thetransmitter. Therefore, the fiexihle cord 2 is constructed, asdescribed, hereinafter, with two concentric conductors,- one of whichshields the other. Further. as also described hereinafter, rubber orother insulating material impervious to moisture and having highinsulation resistance, is preferably interposed between the innerconductor and the outer conductor, to afford high insulation,resistanceand to prevent moisture from setting up irregular leakage paths whichwould result in excessive noise currents. However, the thickness of theinterposed rubber should he as small as is consistent with theattainment of the requisite insulation resistance, so that ,the rubber,wbich has high specific inductive capacity, will not unduly increase thecapacity between tlie conductors` The center of the cord 2 is a fiexibleconductor 20, preferably consisting of a plurality of conducting strandsof tinsel thread.

These strands are not individually shown,

since they are of general type of construction referred to 'in U. S.patents to Sawyer 269,328, DecemberlQ, 1882 and Reed 286,968` October16. 1883, cach strand or tinsel thread being a thread of fibrousmaterial Wound 'helically with metallic tape. These strands are twistedtogether to form conductor 20, which is then served with two layers offioss or a similar insulating material 21., these layers being laid withthe direction of winding reversed. Over these servings is placed aninsulating coating 22 of soft rubber, which', as indicated above, shouldbe as thin as is consistent with the attainment ot the insulatiilmresistance which it must proq vide. Over the rubber is provided aflexible fibrous insulating covering 23, preferably of sill; braiding,the rubber 22 and the braiding Q3 extending substantially to the ends otconductor Q0.

Over the braiding are applied three flexible fibrous insulating`coverings, 2l, 25 and 2G, preferably of sill; braidings, each extendingbetween the points at which the.

irce conductors of the cord 2 are to emerge from the finished cord, andbeing discontinued at those points. l

Overthe braiding QG is applied a liexible conducting and shieldingbraiding` QT, preferably of gold tinsel thread, this braiding 2Tterli'iinating in a i'ree, closelv braided conductor at each end.

Over the tinse'l braiding 2T is applied a flexible fibrous insulatingcovering 28, preferably of silk braiding, extending out over the baretinsel braided free conductors formed by the ends of the braiding 27.

Over die braidinfr 28 is applied a flexible insulating braiding 29,preferably of silk, terminated in a whipping 30 ofl silk, shellaced, atthe amplifier end of the cord, and, at the other end, extended out overthe braiding 28 as indicated in the drawing, or, if desired, at thelatter end, closely braided and brought ott' from the cord as a staycord or tie cord, from the point where the f'ree conductors emerge fromthe cord, for instance, in the fashion shown in U. S. patent to Kaisling738,545,September S, 1903.

The capacity between the conductors of' the cord preferably should notexceed about a0 micromicrofarads per linear foot. Moreover, the cordshould be as short as is consistent with convenience. A length of aboutten feet has been found suitable in a cir-- cuit of the type shown inthe drawing.

lVhat is claimed is:

1. In combination, a condenser subject to variations of its capacity,corresponding to sound waves, and an electrically conductive cord, saidcord comprising electrically conductive means connected to one electrodeof said condenser, an electrically conductive casing connected tolanother electrode of said condenser and encasing said means, andinsulating means spacin said conductive means from said conductlvecasing suiiciently lo render the electrostatic capacity between saidconductive means and said easing small relative to the variations towhich the capacity of said condenser is subject.

2. In combination, a condenser type telephone instrument and a cord forconnecting said instrument in a circuit, said cord comprising a flexiblecenter conductor, a flexible conductive shield serving as a returnconductor, and flexible insulating material separating said centerconductor from said shield suiiciently to render the capacity of saidcord low compared to that of said transmitter.

In combination, a condenser transmitter and a cord for connecting saidinstrument in a circuit, said cord comprising a flexible centerconductor and a braided tinsel shield sufficiently separated by flexibleinsulating material to' render the capacity 'between said conductor andsaid shield small, compared to that of said transmitter.

it. In combination, a condenser transmitter and a cord for connectingsaid i11- strument in a circuit, said cord comprising a rubber covered,tinsel, center conductor and a braided tinsel shield sufficientlyseparated by a plurality of layers ot' insulating braid to render thecapacity of said cord small compared to that of said transmitter.

5. In combination, a condenser transmitter, an electron discharge devicehaving electrodes, and a cord connecting said transmitter to saidelectrodes, said cord comprising a flexible center conduct-.or and aflexible conductive shield separated by a plurality of' layers offlexible insulation maintainingthe capacity and leakage resistance otthe cord at .such values as to substantially avoid lil)

